Glucose infusions administered at constant rates to conscious dogs induce oscillations in plasma glucose and insulin levels. To test the hypothesis that variations in hepatic glucose production are responsible, we plan to infuse radioactive glucose along with untagged glucose, and to measure plasma glucose specific activity as an index of hepatic production. The question will then remain what drives the liver to release glucose periodically? One possibility is that oscillations in insulin secretion are responsible; we will test this suggestion by infusing glucose at a constant rate into chemically pancreatectomized animals receiving insulin at a constant rate. Another possibility is that either the liver or the pancreas is subjected to periodic neural driving, a possibility we will test by infusing glucose into dogs subjected to nerve sections in a variety of locations.